A Balun-Integrated On-Chip Differential Pad for Full/Multi-Band mmWave/THz Measurements

A set of balun-integrated 100/300 GHz differential on-chip pads for broadband characterization (small/large-signal) of active circuits fabricated in SiGe HBT technology is presented. A general theory of asymmetric coupled-lines in inhomogeneous medium was applied to design a Marchand-like balun consisting of multiple sub-λ/4 long nonuniformly-sized line sections with a close-proximity ground-plane to compensate for the frequency-dependent pad impedance.